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[Do not merge][Flang][OpenMP] Fix OpenMP static scheduling when trip count is zero #766

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[Do not merge][Flang][OpenMP] Fix OpenMP static scheduling when trip count is zero #766

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9132d90
[Flang][OpenMP] Fix OpenMP static scheduling when trip count is zero
mjklemm Dec 5, 2025
005a537
Update test case
mjklemm Dec 5, 2025
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4 changes: 3 additions & 1 deletion clang/test/OpenMP/irbuilder_for_unsigned_static_chunked.c
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Original file line number Diff line number Diff line change
Expand Up @@ -50,7 +50,9 @@ extern "C" void workshareloop_unsigned_static_chunked(float *a, float *b, float
// CHECK: omp_loop.preheader:
// CHECK-NEXT: store i32 0, ptr [[P_LOWERBOUND]], align 4
// CHECK-NEXT: [[TMP3:%.*]] = sub i32 [[DOTCOUNT]], 1
// CHECK-NEXT: store i32 [[TMP3]], ptr [[P_UPPERBOUND]], align 4
// CHECK-NEXT: [[COUNTCOND:%.*]] = icmp eq i32 [[DOTCOUNT]], 0
// CHECK-NEXT: [[UPPERSEL:%.*]] = select i1 [[COUNTCOND]], i32 0, i32 [[TMP3]]
// CHECK-NEXT: store i32 [[UPPERSEL]], ptr [[P_UPPERBOUND]], align 4
// CHECK-NEXT: store i32 1, ptr [[P_STRIDE]], align 4
// CHECK-NEXT: [[OMP_GLOBAL_THREAD_NUM:%.*]] = call i32 @__kmpc_global_thread_num(ptr @[[GLOB1:[0-9]+]])
// CHECK-NEXT: call void @__kmpc_for_static_init_4u(ptr @[[GLOB1]], i32 [[OMP_GLOBAL_THREAD_NUM]], i32 33, ptr [[P_LASTITER]], ptr [[P_LOWERBOUND]], ptr [[P_UPPERBOUND]], ptr [[P_STRIDE]], i32 1, i32 5)
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5 changes: 4 additions & 1 deletion llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
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Expand Up @@ -5377,7 +5377,10 @@ OpenMPIRBuilder::applyStaticChunkedWorkshareLoop(
ConstantInt::get(I32Type, static_cast<int>(DistScheduleSchedType));
Builder.CreateStore(Zero, PLowerBound);
Value *OrigUpperBound = Builder.CreateSub(CastedTripCount, One);
Builder.CreateStore(OrigUpperBound, PUpperBound);
Value *IsTripCountZero = Builder.CreateICmpEQ(CastedTripCount, Zero);
Value *UpperBound =
Builder.CreateSelect(IsTripCountZero, Zero, OrigUpperBound);
Builder.CreateStore(UpperBound, PUpperBound);
Builder.CreateStore(One, PStride);

// Call the "init" function and update the trip count of the loop with the
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